1. Field of the Invention
The present invention relates to network entry and initialization of terminal, and more particularly, to a method of transmitting/updating system informations. Although the present invention is suitable for a wide scope of applications, it is particularly suitable for reducing a time taken to update system informations of terminals.
2. Discussion of the Related Art
Generally, the process for network entry and initialization of terminals in a broadband wireless access system is performed by the terminal each time the terminal turns on its power, misses its cell, or moves away into a new cell.
FIG. 1 is a schematic flowchart of a network entry and initialization process.
Referring to FIG. 1, a terminal (subscriber station: SS) performs the scan for a downlink (DL) channel and then establishes synchronization with a base station (BS) [S110]. This step is performed using a preamble, downlink MAP (DL-MAP) message, DCD message and the like, which are received from the base station.
After completion of the synchronization establishment with the base station, uplink parameters (Tx parameters) are obtained from UCD message [S120].
Subsequently, the terminal performs ranging and also performs automatic adjustments [S130].
The terminal then negotiates basic capabilities with the base station [S140].
After completion of the basic capability negotiation, the base station authorizes the terminal (subscriber station: SS) and then performs key exchange [S150]. This step S150 can be performed only if both of the base station and the terminal support an authorizing policy. So, this step S150 is not mandatory.
Subsequently, the terminal performs a registration procedure on the base station [S160].
Thereafter, such a step as a step S170 of establishing IP connectivity, a step S180 of establishing time of data, a step S190 of transferring operational parameters and the like can be performed according to a presence or non-presence of the supports by the terminal and base station and according to a selection made by the terminal.
FIG. 2 is a flowchart for a downlink synchronization process of a terminal.
FIG. 2 shows a detailed flow of the downlink synchronization step S110 with a base station, which is the first step of the network entry and initialization process.
Referring to FIG. 2, a terminal searches a random channel (e.g., ith channel) for a Preamble [S210]. And the terminal then starts to detect a preamble until finding a valid downlink signal [S220].
If the preamble is detected [S220], the terminal matches physical synchronizations of frequency, time and the like using the detected preamble. If the terminal receives a DL-MAP message [S230], timers T1 and T12 are set to start [S240, S250] and MAC synchronization is established [S260].
Meanwhile, if the terminal fails to detect the preamble or fails to receive the DL-MAP message, the terminal moves away into a next channel [S235] and then repeats the preamble detecting step S210.
FIG. 3 is a flowchart of a process for maintaining the downlink synchronization shown in FIG. 2.
Referring to FIG. 3, if a terminal successfully receives DL-MAP and DCD messages within the Lost DL-MAP Interval and T1, respectively [S310], the terminal maintains downlink synchronization and resets a corresponding timer [S320]. In this case, ‘T1’ can be represented as Formula 1.T1=5×DCD interval maximum value  [Formula 1]
In Formula 1, the DCD interval maximum value is defined as 10 seconds. If the terminal fails to receive any one of the corresponding messages until the timer associated with each of the messages expires, the terminal starts a search for a new downlink signal [S330].
FIG. 4 is a flowchart of a process for a terminal to obtain uplink associated parameters.
FIG. 4 shows a detailed flow of the second step in the network entry and initialization process, i.e., the step S120 of receiving the uplink associated parameters as shown in FIG. 1.
Referring to FIG. 4, a terminal preferentially establishes downlink synchronization with a base station [S410] and then waits for UCD message to obtain information relevant to uplink.
If the UCD message is not received until a timer T12 expires, or if the corresponding received information is not suitable for the terminal, the terminal attempts to perform a first step of the network entry and initialization, i.e., a downlink channel searching step S480 again. In this case, the timer T12 can be represented as Formula 2.T12=5×UCD interval maximum value  [Formula 2]
In Formula 1, the UCD interval maximum value is defined as 10 seconds.
If the terminal receives the UCD message before the timer T12 expires [S420], the terminal waits for UL-MAP message for a selected channel. In this case, if an uplink channel is available [S430], the terminal obtains uplink parameters [S440], resets the timer T12 [S450], and then maintains uplink information [S470].
FIG. 5 is a flowchart of a process for maintaining the uplink associated parameters shown in FIG. 4.
Referring to FIG. 5, if a terminal successfully receives UL-MAP and UCD messages within given times, i.e., the Lost UL-MAP Interval and T12, respectively [S510], the terminal maintains valid uplink information and resets a corresponding timer [S520].
Meanwhile, if the terminal fails to receive any one of the corresponding messages until the timer related to each of the messages expires, the terminal determines that the uplink relevant information is not valid and then deletes uplink channel parameters [S530].
Subsequently, the terminal starts a search for a new downlink signal [S540].
FIG. 6 is a signal flowchart of a process for network entry and initialization according to a related art.
In particular, FIG. 6 shows the flow of messages generated in the course of performing steps before a terminal performs ranging. In this case, assume that DL-MAP and UL-MAP are transmitted every frame by setting a frame continuance interval to 20 ms. And, assume that each of the DCD and UCD transmission intervals is set to 10 s which is the maximum value defined in the related art.
Referring to FIG. 6, a base station transmits a preamble, DL-MAP and UL-MAP every 20 ms [S601, S602]. After a power of a terminal has been turned on [S603], the terminal is unable to recognize other messages except the preamble despite receiving the messages [S604].
The terminal is not able to enter a synchronized status [S606] until receiving the preamble and the DL-MAP [S605]. The terminal in the synchronized status then waits for a DCD message transmitted from the base station, even when a UCD message is received [S607]. The terminal receives the DCD message [S608], obtains parameter associated with downlink [S609], and then waits for a UCD message transmitted from the base station.
The terminal receives the UCD message [S610], obtains parameters associated with uplink, and then waits for information of a resource allocated to the initial ranging [S612].
Once the terminal obtains such resource information via the UL-MAP and the like [S613, S614], the terminal transmits CDMA code according to an initial ranging performing procedure [S615].
The conventional terminal has to sequentially read the preamble, the DL-MAP, the DCD, the UCD and the UL-MAP to perform the ranging. Considering the fact that the maximum transmission interval of each of the DCD and UCD is 10 s, this scheme may be inefficient in aspect of the time taken to perform the network entry and initialization process of terminals.
FIG. 7A is a diagram of a UCD updating process according to a related art.
In FIG. 7A, assume that UL-MAP is transmitted every frame by setting a frame continuance interval to 20 ms. And, assume that a UCD transmission interval is set to a maximum value 10 s that is defined in ‘Chapter 10, Global values of 802.16 Rev2’. And, a terminal has already received UCD of which configuration change count is ‘i’.
Referring to FIG. 7A, a base station transmits UL-MAP, of which UCD count is ‘i’, every 20 ms [S701, S702]. The base station retransmits a UCD message, of which configuration change count is ‘i’, at a timing point for transmitting a UCD message [S703].
A terminal receives this message, decodes the received message, and then compares the configuration change count of the newly received UCD to that of the UCD already given to the terminal. If the configuration change counts are equal to each other, the terminal ignores system information within the newly received message [S704].
The base station keeps transmitting the UL-MAP, of which UCD count is ‘i’, every 20 ms [S705]. If the system information is changed [S706], the base station transmits a configuration change count ‘i+1’ and a changed UCD message at a corresponding transmission timing point [S707].
The terminal receives this message and the like, decodes the received message, and then compares the configuration change count of the newly received UCD to that of the UCD already given to the terminal. If the configuration change counts differ from each other, the terminal decodes and stores system information included in the newly received message [S708].
Even when UCD count is changed, the changed system information according to the changed UCD count may be applied in the system after a certain time. That is, the base station may keep transmitting the UL-MAP, of which UCD count is ‘i’, every 20 ms [S709, S710]. The base station retransmits the formerly transmitted UCD message at a corresponding transmission timing point and starts a UCD transition interval timer [S711]. If this timer expires, the base station transmits a UL-MAP of which UCD count is ‘i+1’ [S712].
The terminal receives this message, deletes previous UCD system information, and then applies new UCD system information [S713].
As mentioned in the above description, the base station transmits the system information carried on a single message every long interval. According to this scheme, each terminal needs to decode a message each time to recognize a presence or non-presence of update of system information. And, the terminal has to store and update the system information unnecessary to be updated. Moreover, a time taken for the terminal to apply the changed system information may be increased.